This invention relates to a stator coil including serially-connected conductor segments for an electric rotary machine and also relates to its manufacturing method.
A conventionally proposed stator coil consists of numerous conductor segments which are inserted into slots of a stator core and serially connected to each other. For example, Japanese Patent No. 3118837 discloses a method of manufacturing this type of coil which includes U-shaped conductor segments being serially connected.
According to this kind of serial-joint segmental stator coil, a pair of legs of a conductor segment is separately inserted into different slots spaced by an angle equivalent to a pole pitch. A protruding part of each leg is bent in the circumferential direction. Then, the distal ends of the legs of different conductor segments are successively joined.
More specifically, the conductor segment consists of a U-shaped (more accurately, a V-shaped) head conductor portion (also referred to as a curved or turning portions), a pair of in-slot conductor portions extending from both ends of the head conductor portion and inserted into different slots from one axial side of a core, and a pair of tail conductor portions protruding out of the slots from the other axial side of the core and extending in the circumferential directions. The distal ends of the tail conductor portions of different conductor segments are joined together. In this specification, the in-slot conductor portion and the tail conductor portion may be collectively referred to as a leg of the conductor segment. Accordingly, the head conductor portions of respective conductor segments cooperatively constitute a head side coil end. The tail conductor portions of respective conductor segments cooperatively constitute a tail side coil end.
Furthermore, Japanese Patent No. 3118837 discloses a small-turning conductor segment and a large-turning conductor segment surrounding the small-turning conductor segment so as to cooperatively constitute a conductor segment set. A total of four legs of the conductor segment set are separately held by two rings coaxially disposed. A pair of legs of each conductor segment is expanded in the circumferential direction by causing a relative rotation between two rings to form head slanting portions.
Furthermore, Japanese Patent Application Laid-open No. 2000-139049 discloses a stator core with numerous slots into which small-turning conductor segments and large-turning conductor segments surrounding the small-turning conductor segments are inserted so as to cooperatively constitute conductor segment sets. A total of four legs of the conductor segment set are separately held by four rings coaxially disposed. A pair of legs of each conductor segment is expanded in the circumferential direction by causing a relative rotation between these rings to form head slanting portions.
Moreover, Japanese Patent No. 3104700 discloses a process of welding a pair of distal end portions of adjacent conductor segments disposed in the radial direction, and also discloses providing an intervening member between two distal end portions of adjacent conductor segments disposed in the circumferential direction.
Hereinafter, a conventional method for manufacturing this kind of serial-joint segmental stator coil disclosed in the above-described prior art documents will be explained.
First, a required number of pine-needle shaped conductor segments are prepared. Next, each pine-needle shaped conductor segment is configured into a U-shaped conductor segment with a pair of in-slot conductor portions angularly spaced by one pole pitch in the circumferential direction. Then, the U-shaped conductor segments are spatially disposed (more specifically, aligned in the circumferential direction) so that a required number of conductor segments are simultaneously inserted into the slots of the stator core. For the above-described process, it is possible to use a pair of coaxial rings having insertion holes, for example, disclosed in FIG. 3 of Japanese Patent No. 3118837. According to the manufacturing process shown in this prior art, both legs of a pine-needle shaped conductor segment are separately inserted into two holes of the coaxial rings which are in the same angular position. Then, the coaxial rings are mutually rotated about their axes by the amount corresponding to one pole pitch in the circumferential direction. As a result, each pine-needle shaped conductor segment is configured into a U-shaped conductor segment with a head portion straddling so as to form, as a whole, a U shape (or V shaped) in the circumferential direction.
Next, a process of inserting respective conductor segments, formed into a U-shaped configuration and aligned in the circumferential direction, into corresponding slots of the core is performed. This process is performed by pulling the legs out of the rings having insertion holes, while holding the head conductor portions of respective conductor segments each being formed into a U-shaped configuration and aligned in the circumferential direction, and then inserting the legs of respective conductor segments into slots of the core.
Next, a process for bending each tail conductor portion protruding out of the slot in the circumferential direction is performed. Preferably, each tail conductor portion is bent in the circumferential direction by a half pole pitch. Such circumferential bending process is performed by using a plurality of coaxial rings having insertion holes, for example, disclosed in FIGS. 4 and 5 of Japanese Patent No. 3196738. The distal ends of respective tail conductor portions are inserted into insertion holes of the coaxial rings. Then, each coaxial ring is rotated in the circumferential direction by a half pole pitch (electric angle of π/2), so that each tail conductor portion is bent in the circumferential direction by a half pole pitch. When each coaxial ring is rotated in the circumferential direction, it is preferable to urge the coaxial ring in the axial direction so as to advance toward the tail conductor portion. The radius of curvature at the bend point can be enlarged. Next, the process of welding the distal end portions of the tail conductor portions is performed according to the predetermined order.
Through the above-described processes, an endless phase coil, as a coil representing one of the phases, is formed. To form leader terminals of each phase coil at the head side, one of the U-shaped head conductor portions of the U-shaped conductor segments is cut at an appropriate position. When the leader terminals are formed long enough, the leader portions can be bent in the circumferential direction so as to provide a connecting wire for a neutral point. The reason why such leader terminals are formed at the head side coil end is to avoid the interference with the welding operation performed at the tail side coil end.
The above-described conventional serial-joint segmental stator coils are preferably used for automotive alternators.
However, the above-described serial-joint segmental stator coils have the following problems.
If other distal end pairs are located closely to distal end pairs to be welded, the other distal end pairs will interfere with the welding operation. The welded portion of the distal end pairs will swell in the radial direction. The conductor segments, except the distal end portions to be welded, are sheathed by an insulation film. Due to welding heat, the insulation film may be softened at the slanting portion located closely to the welded portion. If the insulation film is fused, it will sag downward. The fused insulation film will merge or integrate with a neighboring insulation film. The insulation ability will worsen. The coil may cause short-circuit locally.
Assuring sufficient electric insulation is very important for an automotive drive motor which incorporates the serial-joint segmental stator coil to be operated under a high voltage.
To eliminate of the above-explained problems, it is necessary to secure sufficient radial gap between adjacent distal end pairs.
However, according to the above-described arrangements of conventional serial-joint segmental stator coils, enlarging the radial gap between adjacent distal end pairs will require excessively expanding the radial pitches of the conductor accommodation positions in the slot compared with the actual radial size of the in-slot conductor portion. As a result, the space factor of the slot will worsen. The stator diameter will increase. And, the motor size and weight will increase.